1. Field of the Invention
This invention relates generally to air powered devices for dispensing a plastic or viscous material, and in particular to "guns" which can be loaded in situs from bulk materials and immediately dispensed.
2. Description of the Prior Art
Caulking guns to dispense plastic materials through nozzles have been extensively used -- particularly since the manufacture of pressurized aircraft was first instituted. Within the last two decades, the techniques and equipment developed for aircraft caulking and sealing with polysulfides have been increasingly utilized in the construction industry.
Because the materials dispensed in sealing aircraft tended to "set up" relatively soon after they were dispensed, it was generally the practice to provide the materials in cylindrical plastic or cardboard cartridges which could be readily inserted in a sleeve-like barrel of the "guns" initially developed. These cartridges usually included a plastic piston which constituted a closure for the back end of the cartridge. Plastic nozzles of different sizes and configurations could be screwed on to the forward end of the cartridges.
Because the polysulfide or other material is quite tacky and sticks to almost any surface, then later quickly sets up as a rubber-like material, the practice in both the aircraft and construction industries has been to treat the cartridge containers, pistons and nozzles as throw-away items. They have not, however, been of such low cost that when many of them are used and discarded, the expense thereof may be ignored from an economic standpoint. In addition, it costs something to fill the cartridges from a source of bulk material. Moreover, if, after being filled, the cartridges are not used within a certain period of time -- varying depending upon whether the materials are well or poorly sealed in the cartridges -- the material may set up within the cartridge itself and thereupon become removable. This could be very costly as the material itself is not inexpensive.
The expense considerations have proven to be much more of a factor in the construction industry where far greater amounts of caulking compounds may be dispensed and building costs for a given size are not expected to compare at all with the costs of constructing a jumbo or even smaller military or commercial aircraft.
Within the last few years, therefore, some effort has been made to develop and market a gun which could be loaded in situ from a bulk container of a caulking compound. One such gun, known as the MONO Power Gun (Bulk) has been marketed by the Tremco Manufacturing Company of Cleveland, Ohio. This MONO gun, which bears only the number of a Danish patent NR 68-508 appears to be constructed in the manner disclosed in U.S. Pat. No. 3,254,806 issued June 7, 1966 to Niels Kirstein Madsen. The gun of this patent operates on the same principle as does the earlier caulking gun disclosed in U.S. Pat. No. 2,692,706 issued Oct. 26, 1954 to C. J. Wiksten and the earlier grease gun disclosed in U.S. Pat. No. 1,210,179 issued Dec. 26, 1966 to W. H. Lewis.
As far as can be ascertained, guns constructed in accordance with either the Madsen or Wiksten patent have not been widely used in the United States, despite the need for a gun which can be loaded from bulk containers of caulking compounds. Several reasons appear to account for the fact that such earlier guns have not been extensively used in the United States despite a pressing need for a bulk material loadable gun of this general type.
In the first place, they are expensive to manufacture.
Secondly, each has an intricate valving system operated by the single trigger which valving system appears to have been difficult to maintain in reliable operating condition, and, if the trigger should be inadvertently pushed in the wrong direction when the gun is being used to caulk, a suction may be created which could mar the bead of compound which is being extended and even collapse the plastic nozzle from which the material is being dispensed.
Thirdly, it is difficult to clean the gun after use. It is expected that, upon loading, the dispensing barrel will be sucked down into the bucket or can of compound to where it hits the bottom. This means that the entire outside of the barrel to the depth of the container will be covered with the compound and either must be wiped off immediately or it will get on the operator's hands and the swinging closure and even the surfaces adjacent the line where the caulking is in progress. The MONO gun has not thus, been very popular among workmen users.
In addition, if the gun must be disassembled, it is difficult to reassemble because of the intricacy of the valving system. Thus, in the case of the Madsen patent gun, since the handle is detachable from the socket piece and in reassembling it is necessary to properly align the three bores in the socket piece after two units are replaced and one hose connection is made. Thus, reassembly can generally be accomplished only by one who is quite knowledgeable of the Madsen gun details.
Further, because there is a vent hole in the Madsen gun which extends through the piston rod into the forward barrel where the caulking compound may line the inner wall, that vent hole may become clogged with the compound, particularly on the suction stroke.